In recent years, there have been presented gaze-path input interfaces and the like which utilizes an eye movement of a human. Methods for detecting an eye movement includes: an EOG that utilizes a potential generated between a cornea and a retina; a corneal reflex method that detects a movement of a virtual image generated inside a cornea by irradiating a spotlight on an eyeball; a strong-reflection method that uses a difference in reflectance between the cornea and the retina; a method using contact lenses; and so on.
Here, the EOG is a method for detecting an eye movement that utilizes the fact that a human cornea is charged positively with respect to the retina. More specifically, electrodes are placed near a human eyeball and a change in a potential measured by the electrodes is used to detect the eye movement. FIG. 36A and FIG. 36B show examples of the method for detecting an eye movement which utilizes the EOG. FIG. 36A and FIG. 36B are examples of the case where an electrode is placed to the outside and the inside of the right eye of a user at the same distance away from the center of the eyeball.
Assuming the electro-oculogram generated on the outside electrode A is Va and the electro-oculogram generated on the inside electrode B is Vb, Va and Vb are equal when the eyeball of the user is positioned at the center as in FIG. 36A, and the electro-oculogram Va-b measured becomes 0V. On the other hand, in the case where the user looks to the right as in FIG. 36B, the electrode A becomes closer to the cornea of the right eye, and thus Va becomes greater than Vb and the measured electro-oculogram Va-b indicates a plus value. Conversely, in the case where the user looks to the left, Va becomes smaller than Vb and the measured electro-oculogram Va-b indicates a minus value. Thus, it can be observed that the user has moved the eye, to the right when the measured electro-oculogram Va-b indicates the plus value, and to the left when the measured electro-oculogram Va-b indicates the minus value. In the EOG method, an eye movement of a user is detected by utilizing such changes in the measured electro-oculogram Va-b as described above.
When identifying the gaze-point of a user by detecting an eye movement with use of the EOG, it is necessary to calibrate an electro-oculogram that has been generated and the gaze-point of the user at the time. An example of methods for calibrating the gaze-point of a user and a generated electro-oculogram in a real space includes techniques described in Patent Literature 1 and Patent Literature 2 as described below.
With the calibration method disclosed by the Patent Literature 1, an arbitrary calibration pattern is displayed on a display at the time of calibration. Then, data on eye movements in a horizontal and a vertical direction at the time when a user sees the calibration pattern is obtained, and a calibration coefficient is obtained using the data. A method for obtaining the eye movement data includes: a method using corneal reflex; a method using a difference in reflectance between the cornea and a retina; a method using contact lenses; the so EOG that utilizes a potential generated between the cornea and the retina, or the like.
With the calibration method disclosed by the Patent Literature 2, an electro-oculogram of a user is detected, and a mouse cursor on a display is operated by using the detected electro-oculogram. A sight index is displayed sequentially at various positions on the display and a user gazes the sight index to measure the electro-oculogram at this time. Then, the result of this measurement is used for calibration.